Add travis testing

[jfontan]

It depends on #26. I can rebase the PR after it is merged.

It is based on go-billy-gluster testing. The bulk of work is done in test_setup.sh:

• Start a docker container with gluster server from https://hub.docker.com/r/gluster/gluster-centos/
• Redirect needed ports to localhost
• Adds the hostname of the machine to the container so the client can resolve the name
• Creates a test volume with needed permissions

I've also changed the place of the testing logs so root permissions are not needed.

Adding the repository to a travis account should be enough. No other configuration is needed. You can check a test run from my travis account:

https://github.com/jfontan/gogfapi/runs/39555086

[jfontan]

Ah, it seems that travis is already enabled :tada:

[jfontan]

@kshlm rebased

[kshlm]

Thanks!